The overall objective is to elucidate the mechanisms that regulate alpha-fetoprotein gene expression during ontogenesis and hepatocarcinogenesis. By using mRNA-cDNA hybridization techniques, we have found that the expression of AFP gene decreases dramatically during development of rat liver. Also, it appears that glucocorticoids inhibit AFP synthesis at the level of transcription. We propose: a) to continue to determine the expression of AFP during liver development; to ascertain the molecular events responsible for the suppression of the AFP gene in newborn rat hepatocytes by hormones; c) to determine when the reinitation of AFP gene expression occurs following partials hepatectomy and induced hepatocarcinogenesis.